Generally, MIMO (multi-input multi-output) technique means a method of improving transceived data efficiency by adopting MIMO transmitting antennas and MIMO receiving antennas instead of a single transmitting antenna and a single receiving antenna. If a single antenna is used, a receiving side receives data via a single antenna path. If multi-antennas are used, a receiving side may be able to receive data via several paths. Therefore, data rate and throughput can be improved and coverage can be increased. Single-cell MIO operation can be categorized into SU-MOMO (single user-MIMO) scheme for a single user equipment to receive a downlink signal in one cell and MU-MIMO (multiuser-MIMO) scheme for at least two user equipments to receive a downlink signal in one cell.
Meanwhile, many ongoing efforts are made to research and develop coordinated multi-point (CoMP) system to improve throughput of a user on a cell boundary by applying improved MIMO transmission in multi-cell environment. If the CoMP system is applied, it may be able to reduce inter-cell interference in multi-cell environment and to improve overall system performance.
CoMP scheme may be categorized into JP (joint processing) scheme for enabling downlink data to be shared with all CoMP coordinating cells to be transmitted to a specific user equipment and CBF (coordinated beamforming) scheme having downlink data exist in one cell only. The JP scheme may be categorized again into JT (joint transmission) scheme for enabling all coordinating cells to join a signal transmission and CSL (cooperative silencing) scheme for one cell to join a signal transmission only in a manner that the rest of cells stop signal transmission to reduce interference. In the CBF scheme, each coordinating cell, which does not transmit a signal to a user equipment, is able to reduce inter-cell interference in a manner of determining a beamforming matrix of a user equipment, which receives a signal from the corresponding coordinating cell) to apply a less amount of interference to the corresponding user equipment.